Generally, backlash occurs in a movement mechanism which uses a gearbox. Therefore, in a case of such the mechanism which requires accuracy on positioning in a view point of a function of the mechanism, a mechanism and a control, on which influence of the backlash is taken into consideration, are needed.
For this reason, firstly, the backlash is measured with a software control and a corrected value on position is calculated. Next, a method for removing the backlash through feeding back the corrected value on the position to a position control process with the software control is known.
As the above-mentioned method for correcting the position of the subject to be moved with the software control, a method for correcting the position of the subject to be moved in the case of driving by a gearbox which uses a stepping motor will be described with reference to FIG. 1.
The stepping motor is rotated on the basis of number of applied pulses. For this reason, a rotary drive by the stepping motor can realize the correct position control for the subject to be moved.
In an operation of correcting a position of the subject to be moved with the software control, firstly, the subject to be moved is moved to a position of an original point by the gearbox, and an original point reset is carried out at the position (Step S1). Then, the subject to be moved is moved by a distance, which is corresponding to 25 pulses, in a plus direction from the reset position of the original point (Step S2), and number of pulses “A”, which are required for returning the subject to be moved to the original point, is counted (Step S3). Moreover, with the software control, the subject to be moved is moved by a distance corresponding to 25 pulses in a minus direction from the position of the original point (Step S4), and number of pulses “B”, which are required for returning the subject to be moved to the original point, is counted (Step S5).
A difference between the measured value and a theoretical value (feeding pulse) in the plus direction and a difference in the minus direction are calculated by use of the measured values “A” and “B” which are obtained in this way, and an average value of the differences is defined as backlash (XB). When the above is expressed in a formula, the formula is shown as follows:XB—A=|pulse “A”|−25 pulse,XB—B=|pulse “B”|−25 pulse, andBacklash(XB)=(XB—A+XB—B)/2.
A pan-tilt camera, which corrects a position of a subject to be moved with the software control mentioned above and which corrects backlash in a drive mechanism, is known (for example, refer to patent literature 1).